Loop with Recursive Types

In this section, we will explore how to create a loop with recursive types in TypeScript. We will start by defining a simple recursive type and then show how to create a loop with it.

Recursive Types

Basic recursive types are types that refer to themselves in their definition. For example, consider the following type definition:

type Recursive
<T
> = T
 extends [infer Head
, ...infer Tail
]
 ? [Head
, ...Recursive
<Tail
>]
 : [];

In this definition, the Recursive type is defined in terms of itself. It takes a type T and checks if T extends an array with a head element and a tail element. If it does, it constructs a new array type by recursively applying Recursive to the tail element.

Examples

// This case Tail always be array
type CheckTailStatus
<T
 extends any[]> = T
 extends [infer H
, ...infer T
]
  ? T
 extends any[]
    ? 'Tail is array'
    : 'Tail is not array'
  : 'empty array';

// The result will be "empty array"
type check1
 = CheckTailStatus
<[]>;
// The result will be "Tail is array"
type check2
 = CheckTailStatus
<['hello']>;
// The result will be "Tail is array"
type check3
 = CheckTailStatus
<['hello', 'wolrd']>;

In this example, we define a type CheckTailStatus that checks if the tail of an array is an array or not. We use conditional types to check if the tail element T extends an array. If it does, we return 'Tail is array'; otherwise, we return 'Tail is not array'.

Loop with Recursive Types ​

Recursive Types ​

Examples ​

Loop with Recursive Types

Recursive Types

Examples